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Re: How much solar panel(s)?
Foggy, other DM panels say:
Cells by GinTech
which means they put out 144 watts at a peak voltage of 18 volts with a maximum amperage of 8 amps. If you are using any kind of regulator, even a pwm regulator, that should be reducing your voltage to perhaps 14 volts. Which would leave you with 14 volts at the same maximum of 8 amps, for 112 watts. Your loss of 32 watts, or about 23% of the power, is being thrown away by your controller and ignoring whatever the internal loses are (often quoted at 2-4% for MPPT controllers) that means upgrading to an MPPT controller could give you a fast 20% more power from the same panels. If your batteries are discharged, and your controller is putting out 12.5 volts instead of 14 volts, your controller is throwing away even MORE power and the MPPT gain is even greater. And that's going to be the case most of the time.
Is that worth $400? Dunno, can you live with what you have, do is that difference enough so that you don't have to buy another panel to keep the batteries topped up? That's a subjective choice to make.
If you can find curves from DMSolar that show amperage output versus voltage output, you can compare to see if this 20% difference (which is based on full light, i.e. the two hours around noon) gets bigger or smaller during the rest of the day.
Of course, with Amazon's generous returns policies, I'd say that IF you can afford an MPPT controller, buy one with the next two panels. Run two with the MPPT, two with the PWM, and use a charge monitor or a little ingenuity to actually compare what each system is giving you. Math is all well and good, but I like to see systems run side by side with realworld comparisons.
If the MPPT kicks ass and gives you better output, keep it! If it doesn't do much, back it goes. When I ran some tests on an MPPT it took me about two hours to call the maker and ask why the funny numbers I was getting, why it wasn't showing typical "3 stage" voltage changes. It turns out, MPPT can be smarter than that, and designed to maximize the power push at the least voltage needed as well. less acid boiling, higher efficiency...they're impressive to see and measure in action.
Worth the extra cost? Dunno. Is a Ferrari a waste of money? Is four wheel drive? Only one way to find out, right? :-)
Last edited by hellosailor; 08-15-2012 at 12:12 AM.